A ghostly procession of ten volunteers clad in orange safety vests and cellophane-covered headlamps shuffles down the middle of a lonely wooded road in northwestern New Jersey, each staring intently at their feet. It’s a damp March night and the temperature is hovering around 40 degrees Fahrenheit.

These hardy workers are looking for frogs and salamanders to count. They’re waiting for the amphibians to cross the road on their way from the wooded uplands where they winter to the marshy lowlands and vernal pools where they will mate, come spring. The volunteers have been standing out here for nearly three hours, and they haven’t seen a thing. The forest is still — not a single drop of rain to wet the road and entice the frogs and salamanders to make their crossing. “I think we got skunked,” says one bobbing orange vest to the darkness.

These volunteers — two schoolteachers, a computer systems analyst, and a graphic designer among others — comprise the annual New Jersey amphibian crossing survey. On the first rainy, warm (above 40 degrees) night in early spring, they have the town’s permission to close the road to traffic to aid the amphibian migration and take a census of the species crossing the road.

But this night isn’t living up to expectations. Though the local forecast called for a downpour, it isn’t raining tonight or even misting — and the frogs and salamanders are keeping a low profile. Experts are unsure what exactly triggers the spring migration, but rising ground temperatures, dropping barometric pressure and the sound of the raindrops hitting the ground may all play a role. The ground must also be wet to keep the moist amphibian skin from drying out on the journey.

The volunteers expect to see mainly wood frogs and spotted salamanders, common amphibians in northern New Jersey. The abundance of these particular species here is exactly why Mackenzie Hall, a biologist for the Conserve Wildlife Foundation of New Jersey and organizer of the survey, says she is working to protect these populations now. But even relatively common species don’t seem to be as abundant in New Jersey as they used to be. One volunteer, Nancy Schiesl, remembers over 400 amphibians crossing the road in one night when she joined the survey seven years ago — but hasn’t seen such a bevy in years. Data from crossing sites throughout the state suggests that car traffic may be contributing to declines in the Garden State’s migrating amphibian populations.

Though the spotted salamanders and wood frogs of northern New Jersey are not endangered yet, an estimated one third of the world’s amphibians are threatened with extinction, according to the International Union for the Conservation of Nature, or IUCN, an environmental group. A host of factors play a role in global losses, from habitat destruction and road kill, to climate change and the unchecked spread of disease. These threats are converging on amphibians now, jeopardizing the survival and diversity of these ancient vertebrates, with uncertain but potentially far-reaching consequences to the diverse ecosystems in which they live.

“You can’t take the ecosystem apart gently,” says David Wake, a herpetologist at the University of California, Berkley, who explains that because amphibians are a vital part of their habitats, their decline will most certainly be disruptive.

Amphibians evolved from fish and emerged from the water roughly 350 million years ago, making them the oldest living vertebrates to set foot on land. There are currently 6,300 known species worldwide. Collectively, amphibians have persisted through warm and cold periods in Earth’s history and several major extinction events, including the one that killed the dinosaurs. Historically, amphibians are survivors. But their unique physiology and behavior make them one of the most susceptible animal groups to human-related causes of extinction. An estimated 168 amphibian species have disappeared in the last 20 years alone, according to the IUCN.

Habitat destruction, much of it associated with roads, is probably the most serious threat to amphibians worldwide, according to Tom Langen, a wildlife biologist at Clarkson University in Potsdam, New York. Langen has identified amphibian and reptile road kill “hotspots” in New York State. They are usually within 100 meters of a road, and especially at causeways, where there are wetlands on both sides.

At one spot in Morris County, New Jersey, car traffic may have decimated the local population of blue-spotted salamanders, an endangered species in the state, according to Mike Anderson, a coordinator with the New Jersey Audubon Society. The salamanders were no match for the more than 200 cars passing through the site at rush hour. Far less traffic — as few as 26 cars per hour — can cause 50 to 90 percent amphibian mortality at crossing sites, according to Anderson. “In the end, we were only seeing a couple [salamanders] a year, so we finally just gave up,” he says.

Though road mortality may be the cause of local extinctions, “the habitat degradation associated with roads often has greater effects,” says Langen. Along heavily trafficked urban corridors, car exhaust and road salt run-off can leach into neighboring waterways and damage amphibian eggs and tadpoles. Even in rural areas where car traffic is low, roads serve as barriers, slicing large amphibian breeding groups into small, fragmented populations. Amphibians are especially susceptible to pollution because of their unique lifestyles — they spend their time as juveniles in the water and as adults on land, coming in contact with a wide range of air and water pollutants throughout their life cycle.

But loss of suitable habitat does not explain why amphibians are disappearing at an alarming rate in pristine natural areas, like Yellowstone National Park. There, climate change may be to blame. Droughts are more frequent and severe now in Yellowstone than they were a century ago, presumably due to global warming, scientists say. The number of permanently dry ponds in the northern section of the park has quadrupled in the past 16 years alone, causing precipitous declines in the amphibian populations that use those ponds to complete their life cycles, according to Sarah McMenamin, a wildlife biologist at Stanford University who studies the ponds.